1. Field of the Invention
The present invention relates to near field communication (NFC), and more particularly to a NFC system having a plurality of antennas and an associated apparatus.
2. Description of the Prior Art
Near field communication (NFC) technology is designed for short distance wireless communication and now is widely applied to our daily life. For example, the contact-less radio frequency identification (RFID) card has been applied to the public transportation tickets and the credit card transactions. The NFC technology performs data transmission through inductive coupling. Take a passive (i.e. powerless in itself) RFID card or RFID tag as example: there are coil antennas inside the RFID card and the card reader; the card reader generates an alternating magnetic field by its coil antenna, and the coil antenna of the RFID card inductively couples the alternating magnetic field to generate the electric power required for operation of the circuit within the RFID card. The communication between the RFID card and the card reader is performed by using carriers of high frequency (HF, such as 13.56 MHz) or low frequency (LF, such as 125 KHz) in the spectrum. The RFID card can backscatter its data to the card reader. The card reader can transmits data to the RFID card so as to write the data into the RFID card. In addition to the card reader and the passive RFID card, the near field communication can also be performed by two transceivers. After one transceiver transmits data, the other transceiver makes a reply in a predefined format. For example, two cell phones can transmit data to each other by means of the NFC technology.
In prior arts, an application is developed by using the NFC technology to enable the wireless communication between a computer and a RFID card or cell phone. The coil antenna used for the near field communication is wound around a display panel. When a user moves the RFID card or cell phone close to the display panel wound with the coil antenna, the RFID card or cell phone can be inductively coupled to a RF module connected to the coil antenna, so as to transmit data to the RF module, which then transmits the data to the computer so as to display the data on the display panel. FIG. 1 and FIG. 2 show a vertical view and a lateral view of an example of this application. When two cell phones 15,16 (or RFID cards) approach a touch sensitive display panel 11, a RF module 13 is inductively coupled to the cell phone 15,16 by an alternating magnetic field (shown as the magnetic power lines) generated by an antenna 12. The user can operate the touch sensitive display panel 11 to instruct a host computer 14 to transmit the data of the cell phone 15 to the cell phone 16. Therefore, after the RF module 13 and the cell phone 15 finish handshaking, the cell phone 15 transmits its data to the host computer 14 via the RF module 13; after the RF module 13 and the cell phone 16 finish handshaking, the host computer 14 sends the data to the cell phone 16 via the RF module 13.
However, in the above application, the antenna 12 is wound around the touch sensitive display panel 11. Thus, when the touch sensitive display panel 11 and the wound antenna 12 become larger, the area of the coil antennas within the cell phones 15,16 (or RFID cards) become smaller in comparison with the area of the antenna 12, and thus the number of the magnetic power lines which can be captured by the cell phones 15,16 is relatively decreased such that the magnetic field intensity is weakened. In order to enable the cell phone 15,16 to capture enough magnetic field intensity required for communication, the RF module 13 and the antenna 12 must supply more power such as increasing the current passing through the antenna 12 or the number of coils of the antenna 12 so as to generate higher magnetic field intensity. However, this would cause the interference between the electronic components in the touch sensitive display panel 11 and the near field communication, and thus the quality degradation of both display and wireless communication. On the other hand, since the area of the antennas in the cell phones 15,16 becomes relatively smaller against the area of the antenna, the coupling coefficient becomes smaller consequently. This would also degrade the communication quality.
Moreover, in the above application, if multiple cell phones or RFID cards are to communicate with each other via the host computer 14 simultaneously, multitasking efficiency is hard to achieve since the host computer 14 can communicate with the cell phones or RFID cards via only one antenna 12.